Carbonate dissolution during subduction revealed by diamond-bearing rocks from the Alps

The Alps 2: Controls on crustal subduction and (ultra)high‐pressure rock exhumation in Alpine‐type orogens

“…These include, among others ( Figure 1) [see Butler et al, 2013], (1) Eocene accretion/subduction of Piemont-Liguria and Europe-derived terranes to (U)HP P-T conditions of up to~3.5 GPa/760°C [Chopin et al, 1991;Reinecke, 1991;Meffan-Main et al, 2004;Le Bayon and Ballèvre, 2006;Frezzotti et al, 2011;Gasco et al, 2011aGasco et al, , 2011b; (2) subsequent rapid exhumation (~1-3.5 cm/a) of (U)HP rocks to the base of the orogenic crust [Rubatto and Hermann, 2001;MeffanMain et al, 2004;Le Bayon and Ballèvre, 2006;Lapen et al, 2007;Berger and Bousquet, 2008;Gabudianu-Radulescu et al, 2009], accompanied by possibly synconvergent, normal-sense shearing between the exhumed (U)HP and overlying low-pressure crust [Ballèvre and Merle, 1993;Ganne et al, 2006;Reddy et al, 1999Reddy et al, , 2003Rosenbaum et al, 2012;Gasco et al, 2009Gasco et al, , 2013; and (3) final, slower (<0.5 cm/a) transcrustal (i.e., through the orogenic crust) exhumation of (U)HP rocks during orogen-scale bivergent thrusting [Schmid et al, 1987;Rubatto and Hermann, 2001;Meffan-Main et al, 2004;Le Bayon and Ballèvre, 2006].…”

Thermal structure and metamorphic evolution of the Piemont-Ligurian metasediments in the northern Western Alps

“…Much attention has been paid to the metamorphic evolution of the HP to UHP Zermatt-Saas zone because of well-preserved eclogite facies assemblages in metabasites (e.g. Bearth 1967;Ernst and Dal Piaz 1978;Oberha¨nsli 1980;Barnicoat and Fry 1986;Bucher et al 2005), coesite inclusions within garnets in metaradiolarites (Reinecke 1991) and micro-diamonds in metamorphosed seafloor Mn nodules (Frezzotti et al 2011). The Combin zone contains only few relics of blueschist facies assemblages in both metabasites (Ayrton et al 1982;Sperlich 1988;Bucher et al 2004) and metapelites (Pfeifer et al 1991;Bousquet et al 2004), which makes its metamorphic evolution difficult to assess.…”

Geochemistry of primary-carbonate bearing K-rich igneous rocks in the Awulale Mountains, western Tianshan: Implications for carbon-recycling in subduction zone

“…Nevertheless, the CO 2 emitted from volcanic arcs (e.g., Wallace, 2005) and the CO 2 bearing fluids within eclogite-facies rocks under high-pressure conditions (e.g., (Gao et al, 2007)) are considered to be derived from subducted slab. Effective release of CO 2 is likely to require open-system decarbonation, flushing of carbonate-rich rocks by aqueous fluids (Zack and John, 2007) or dissolution of carbonates into slab melts or supercritical liquids (Frezzotti et al, 2011). The participation of fluids (CO 2 + H 2 O) derived from the devolatilization of subducting slabs would reduce the peridotite solidus and play critical roles in the fluxing melting of the mantle wedge and global geochemical cycles Spandler and Pirard, 2013).…”

“…However, the origin of carbonate melts and their relationship to associated silicate rocks is still controversial. In subduction zones, Sr-Nd-Pb and C-O isotopes have been interpreted to indicate that most carbonate melts associated with alkaline igneous rocks were derived from the recycling of subducted carbonate-rich sediments (e.g., Bell and Simonetti, 1996;van Achterbergh et al, 2002;Walter et al, 2008;Marin-Ceron et al, 2010;Frezzotti et al, 2011). Therefore, the occurrence and genesis of primary carbonate-bearing K-rich igneous rocks in the convergent margins can be utilized to help understanding crust-mantle interaction and can provide insights into the mechanisms of carbon-recycling within the mantle wedge during subduction.…”